Support is requested for four lines of research, each of which extends previous studies of human listeners' abilities to process the acoustic details of complex sounds. (1) The limits of normal listeners' ability to discriminate nonspeech patterns will be further investigated, in tests of the Dimension Specific Capacity hypothesis, and in studies of the plasticity of listener's characteristics distribution of auditory attention. (2) Corresponding limits will be studied for speech stimuli, using natural and synthetic vowels. Listeners' abilities to resolve phoneme-relevant acoustic details will be determined for isolated vowels and vowels in sequences, under various levels of stimulus uncertainty. (3) Limits of spectral-temporal resolving power will be determined for hearing-impaired listeners, for speech and nonspeech complex stimuli. An effort will also be made to measure cross-modality (auditory, visual, tactile) temporal processing capabilities, and to determine whether those capabilities may explain differences in speech processing among audiometrically similar listeners. (4) Corresponding limits of processing will be determined for language-disordered children and young adults.